Solenoid operated spray devices, such as those used for directing heated liquid coating materials in can manufacturing operations, typically include a needle valve that is reciprocated between on and off positions through actuation of the solenoid at rates of about 300 to 400 cycles per minute, consistent with the rate of advancement of cans, for successively spraying a coating of heated liquid into or on the cans. It is desirable to adjust the stroke of the needle valve for a particular coating and/or spray application.
Heretofore, effecting stroke adjustment in such spray devices has been cumbersome and sometimes causes damage to the valve needle or seat. One procedure, for example, requires removal of the spray tip, disassembly of a retaining nut, and rotation of a valve seat member relative to the spring biased valve needle to force the valve seat upwardly against the biasing force of the needle thereby changing the position of the valve seat, and hence, the distance the needle travels during each operating cycle, i.e. the stroke. Rotational movement of the valve seat against the needle can scuff or damage the valve seat and/or needle and adversely affect subsequent spray performance.
Furthermore, when the spray device is idled, such as during stroke adjustment or during interruption in the can manufacturing line, coating liquid within the gun will cool, such that upon resumption of the spray operation, the cooled liquid will be below the temperature necessary for achieving optimum spray performance and coating.
Servicing of such solenoid operated spray devices also can be a time consuming and costly procedure, often necessitating uncoupling of fluid supply and return lines, disconnection of electric power, and removal of the spray gun from its mounting. Such service procedures can cause significant interruptions in the high speed can manufacturing line.